The genomic integrity of the zygote is critical for normal embryonic development and birth of healthy baby. The long-term objectives of this research are to identify the maternal DNA repair genes that maintain genomic integrity after fertilization with sperm from fathers exposed to environmental mutagens. It is well established that exposure of male mice to mutagens before mating can induce high frequencies of chromosomal defects detected at zygotic metaphase and that the incidence depends on the genotype of the egg. There is also new evidence that the incidence of chromosomal aberrations in zygotes after paternal exposure is numerically predictive for pregnancy loss and de novo translocations at birth. However, the underlying mechanisms by which zygotes repair environmentally-induced sperm lesions remain poorly understood. Our hypothesis is that qualitative or quantitative limitations in maternal DNA repair are responsible for the zygotic conversion of sperm lesions into chromosomal aberrations and for the differential susceptibility of certain maternal genotypes. Double-strand breaks (DSB) are obligatory intermediates in the conversion of sperm lesions into chromosomal aberrations; we present new data that several gene products involved in DSB repair and other types of DNA repair are present in eggs at fertilization. Aim 1 will determine which of the genes involved in DSB repair are present in eggs by analyses of mRNA and protein by RT-PCR and immunocytochemistry, respectively. Aim 2 will examine the roles of homologous and non-homologous DS repair functions in the zygotic conversion of sperm lesions into chromosomal aberrations by using knockout mice. Cytogenetics will be quantified using a new PAINT/DAPI procedure developed at LLNL to detect both stable and unstable chromosomal rearrangements. The relevance of the type of initial sperm lesion will be investigated by treating males with different germ-cell mutagens and mating them with untreated female mice. Aim 3 will utilize DNA microarrays to determine whether strains of mice that differ in maternal susceptibility to paternally-transmitted chromosome damage have associated differences in zygotic expression of genes from DSB and other DNA repair pathways. The proposed research is important for two reason: (1) towards understanding mechanisms involved in the maternal conversion of environmentally-induced sperm lesions into inherited chromosomal defects, and (2) for identifying maternal "genetic-susceptibility" genes associated with increased risks for pregnancy loss, birth defects, and genetic disease in offspring following paternal exposure to environmental agents.